The electro-hydrodynamic atomization of liquids, or electrospray, has provided an essential tool for the biochemical analysis over the last decades (Electrospray Mass Spectrometry, o ESMS), following the discovery of its potential in the middle 80s. One of the advantages it presents is the small amount of analyte required for the analysis. Nevertheless, in the case of applications requiring the atomization or breakup of a sufficiently large amount of liquids per unit of time, a key limitation of electrospray is its low productivity. Some examples of these applications are to be found in the pharmaceutical industry (active principle encapsulation), food industry (encapsulation of diverse organoleptic ingredients among other), phytosanitary industry . . . In particular, some electrospray applications have arise aiming at the generation of composite jets, with concentrical arrays of diverse immiscible or hardly miscible liquids (Loscertales, Cortijo, Barrero and Gañán 2001, patent request PCT/ES02/00047); such applications are geared to the production of micro-capsules or nano-capsules; however, research is challenged by the need to increase the productivity of the electrospray technology and devices.
On the other hand, the atomization of liquids by purely fluidomechanic means, in particular by pneumatic procedures, is a capital tool in many applications and industrial, technological or scientific developments, having an impact on our daily life. The so-called “Flow Focusing” technology (Gañán-Calvo 1998, Physical Review Letters 80, 285), is based on specific flow geometries and takes the pneumatic option to generate liquid micro-jets which break up into very small drops of essentially homogeneous size. “Flow focusing” is also able to produce liquid micro-jets surrounded by another liquid—rather than by a gas—; alternatively it can produce gas micro-jets surrounded by a liquid, which may play the role of a focusing agent, analogous to the role of the gas in a standard pneumatic device; as a result, micro-bubbles of perfectly homogeneous size are produced.
There are many liquids which cannot be atomized as a result of their physical properties; sometimes, they cannot be combined to the end of forming micro-drops or capsules by electro-hydrodynamic atomization.
The flow-focusing technology, in turn, is limited in that it may require very large atomization pressure when nano-metric sizes are sought. This may prove a handicap in some applications.
Both these disadvantages are overcome by means of the invention disclosed in the Spanish patent request P2002-00286. The invention deals with a non-trivial combination of the electrospray and flow focusing technologies. The result is a procedure allowing the manipulation of a wide parametric spectrum involving diverse liquid properties, liquid flow-rates and drop sizes including combinations that cannot be handled or are hard to handle with any of the two mentioned technologies taken separately: i.e. a low reproducibility or robustness would be observed.